1. Field of the Invention
The invention relates in general to refrigeration systems, and more specifically to refrigeration systems having electrical heaters for defrosting the evaporator coil heat exchanger assembly.
2. Description of the Prior Art
In refrigeration systems, such as transport refrigeration systems for conditioning the air of a truck or trailer hauling fresh or frozen loads, it is common to rapidly defrost the evaporator heat exchanger assembly with electrical heaters when the frost and ice build-up reduces the effectiveness of air flow over the evaporator. The evaporator section of the refrigeration system includes a plurality of refrigerant carrying tubes, often called hairpin tubes, with a large number of thin, closely spaced metallic heat exchanger plates or fins connected to the coolant tubes. The fins are usually wavy or corrugated to increase the surface area for a given heat exchanger volume. Frost builds up on the fins and impedes air flow over the surface of the fins, and it is this frost that must be periodically removed.
U.S. Pat. No. 3,786,227, which is assigned to the same assignee as the present application discloses periodically replacing spaced groups of fins across the heat exchanger assembly with relatively thick metallic plates, each of which has an electrical heating element attached thereto. While this is highly effective, it requires modification of the heat exchanger unit at the time of manufacture, and adds significantly to the manufacturing cost.
Another prior art approach holds an electrical heating element against the edges of the fins with a plurality of spaced metallic channel members, each of which extends across the two legs of a U-shaped electrical heating element. Each channel member includes two spring loaded fasteners, with each spring loaded fastener including a hook, a helical spring, and two large washers. While this approach does not require modification of the heat exchanger at the time of manufacture, the channel shaped device is relatively costly to manufacture and is awkward for one assembler to install. In a transport refrigeration system the evaporator heat exchanger is elevated, requiring an installer to work from below the unit. The heating element must be held against the edges of the fins which make up the lower surface of the heat exchanger, the metallic channel must be placed over the two legs of a heating element, and the two spring loaded fasteners must each be threaded up between two closely spaced wavy heat exchanger fins and attached to a coolant tube. The channel must usually be moved or adjusted along the heating element after the initial placement, until the fasteners are properly aligned with a coolant tube.
Thus, it is an object of the present invention to provide new and improved arrangement for disposing electrical heating elements in heat conducting relation with the fins of an evaporator heat exchanger assembly of a transport refrigeration system. The new and improved arrangement should not require modification of the heat exchanger assembly, it should have a lower manufacturing cost than prior art arrangements, and it should make it easier and quicker for a single installer to initially install and to replace electrical heating elements in heat exchange relation with the fins of an evaporator heat exchanger assembly.